<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .container{
            height: 40px;
        }
        /* PC min-width:992px; */
        /* @media是查询设备 */
    @media (min-width:992px){
        .container{
            width:1170px;
            background: red;
        }
    }
    /* iPad 大于768px
    小于 992px */
    @media(min-width:768px)and(max-width:992px){
        .container{
            width:750px;
            background: blue;
        }
        
    }
    /* iphone 小于768px */
    @media(max-width:768px){
        .container{
            width:375px;
            background:yellow;
        }
    }
    </style>
</head>
<body>
    <!-- pc 1170px bg red  -->
    <div class="container"></div>
    
</body>
</html>